In-situ IR studies of surface species during the selective catalytic reduction (SCR) of NO by propene over Cu-ZSM-5 zeolites

Abstract

The intermediate formed during the SCR of NO by propene over Cu-ZSM-5 were identified and their activities were measured using FTIR. The band at 1624 cm(-1) assigned to NO2 species adsorbed on Cu(II) was observed after exposing Cu-ZSM-5 to NO or NO and O-2 at 350 degrees C. The band al 2250 cm(-1) assigned to -CN and/or -NCO species was observed during the SCR at 350 degrees C. The NO2 species adsorbed on Cu ions was reduced to produce Nz by the reaction with propene. When -NCO was exposed to NO and O-2 at 400 degrees C, the rate of formation of the band at 1624 cm(-1) was much faster than that of decrease of the band at 2250 cm(-1), indicating that the site for NO2 formation is different from the site occupied by -NCO. The -NCO identified by the band at 2250 cm(-1) was involved in the slow catalytic cycle, while the NO2 species was involved in the fast catalytic cycle.